For many people "Telemarketing" and "Telesales" are inter-changeable descriptions for the role of sales lead generation and appointment setting.
I suppose, strictly speaking, you could describe them as:
Telemarketing - conducting marketing research, surveys, data-cleaning and generating marketing leads by telephone.
Telesales - actually closing business over the phone.
These are two extremes with telemarketing being the softer end of the spectrum and telesales being the sharper end (we clearly see ourselves at as the latter)
However, I've found that when most people are talking about "telesales" they're thinking about someone who's making calls to either generate leads or set up sales appointments.
Essentially, telemarketing and telesales are both seen as part of the sales process.
Interestingly, Wikipedia currently describes Telemarketing as follows:
Telemarketing (known as telesales in the UK and Ireland) is a method of direct marketing in which a salesperson solicits to prospective customers to buy products or services, either over the phone or through a subsequent face to face or Web conferencing appointment scheduled during the call.
I thought the "known as telesales in the UK and Ireland" was interesting.
Certainly, I know a number of US based "telemarketers" who would always consider themselves salespeople, so maybe Wikipedia's got that one right.
Either way, whether it's telemarketing or telesales, it's always about the same thing - opening doors and closing deals.